Magnetization reversal of FePt based exchange coupled composite media

Microstructure and magnetic properties of L1(0)-ordered FePt-C nanogranular films capped with A1-disordered FePt layers with various thicknesses were investigated. After the growth of 9.5 nm thick L1(0)-FePt-C granular layer on a MgO(001) single crystalline substrate at a substrate temperature of T-s = 600 degrees C, FePt capping layers with thicknesses, t(FePt), ranging from 2.7 to 8.6 nm were deposited at T-s = 400 degrees C. The coercivity of the L1(0)-FePt-C/A1-FePt exchange coupled composite (ECC) media decreased from 4.9 to 1.4 T with increasing t(FePt). Evaluation of energy barrier, E-b, using the Sharrock equation indicated no degradation of thermal barrier in spite of the large reduction in the coercivity. The switching field distribution of the ECC media is significantly reduced from 23% for the single layer FePt-C granular film to 8% for the ECC media with t(FePt) = 6.5 nm. Micromagnetic simulations showed the magnetization reversal of ECC media with t(FePt) = 2 nm capping layer occurs by the coherent rotation while domain wall pinning becomes dominant for t(FePt) >= 5 nm. The switching field distribution (SFD) of the ECC media is substantially decreased for t(FePt) = 2 nm. Low coercivity with high Eb and improved SFD observed from the ECC media makes them promising as high areal density recording media for both perpendicular magnetic recording (PMR) and heat assisted magnetic recording (HAMR). (C) 2016 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.